1. Field of the Invention
The present invention relates to a display device, and more particularly, to a flat-face panel display device which sets the pressure in a sealed space defined in the inside of display device lower than the outside pressure.
2. Description of the Related Art
As a display device which exhibits high brightness and high definition, a color cathode ray tube has been widely used. However, along with the progress in the field of information processing equipment and to realize the high quality television broadcasting, the demand for a flat-plate-like display (panel display) which exhibits excellent characteristics such as high brightness and high definition, is light-weighted and can minimize the space has been increasing.
As typical examples, liquid crystal display devices, plasma display devices or the like have been commercialized. Particularly, as display devices which can further enhance high brightness, panel-type display devices of various types such as field emission displays (also referred to as xe2x80x9cFEDsxe2x80x9d hereinafter) or organic EL displays which are characterized by the low power consumption are expected to be commercialized soon.
Among such panel-type display devices, in a display device which makes a sealed space defined between two panels consisting of a front surface panel and a back surface panel have pressure lower than the ambient atmospheric pressure or a vacuum state, it is necessary to hold a gap between these two panels at a given value and to maintain the air-tightness of the sealed space. To form the sealed space in the gap defined between two opposing panels, it is necessary to insert spacers between inner walls of peripheries of both panels. These spacers may be obtained by coating an adhesive agent (such as a frit glass or the like) using a dispenser, a multiple printing or the like. However, when the gap between both panels is large, it is difficult for the spacers having such a constitution to maintain a given gap since the adhesive agent flows and is deformed. On the other hand, the multiple printing is time consuming.
For example, with respect to the FED having the large gap between both substrates, glass plates are used as the panel material and the gap of the sealed space defined between these glass plates (the front surface panel and the back surface panel) is approximately 1 mm or more. The above-mentioned gap can be formed by fixedly securing the front surface panel and the back surface panel with the outer frame using the adhesive agent.
FIG. 6 is a schematic cross-sectional view for explaining a constitutional example of a field emission display device (FED) as an example of the panel display device of this type. In this field emission display device, peripheral inner walls of a back surface panel 1 and a front surface panel 2 are fixedly secured to each other by means of an outer frame 3, thus forming a sealed space which is at a reduced pressure or is evacuated in the inside surrounded by the outer frame 3. The thickness of the outer frame 3 is set to approximately 1 mm and is fixedly secured to the back surface panel 1 and the front surface panel 2 using an adhesive agent 4.
A cathode electrode 5, an insulation layer 6 and a grid electrode 7 are formed on an inner surface of the back surface panel 1, while an anode electrode 8 and a phosphor 9 are formed on an inner surface of the front surface panel 2. The cathode electrode 5 and the phosphor 9 form a pair and constitute one pixel. In case of a color display, one color pixel is constituted of a group made of three neighboring different phosphors which irradiate lights of different colors (generally, red, green and blue). Here, a partition wall 10 made of insulation material is disposed between respective pixels.
In the FED of this type, electron beams irradiated from the cathode electrode 5 are controlled in response to image information applied to the grid electrode 7 and impinge on the phosphor 9 laminated on the anode electrode 8 thus generating given colors.
FIG. 7 is a developed perspective view for schematically explaining a conventional constitutional example of the back surface panel, the front surface panel and the outer frame shown in FIG. 6. The outer frame 3 which is interposed between the back surface panel 1 and the front surface panel 2 is formed of an integral or unitary frame. By coating adhesive agents 3a, 3b which are preferably made of frit glass on respective surfaces of the outer frame 3 which face the inner surfaces of the back surface panel 1 and the front surface panel 2 in an oppose manner using suitable means such as printing or the like, the back surface panel 1 and the front surface panel 2 are fixedly secured to each other thus forming an inner space which constitutes the sealed space which is at a reduced pressure or in a vacuum state.
As literatures which disclose the display devices of this type, Japanese Laid-open Publication 21335/2000, Japanese Laid-open Publication 22782/1996 and the like can be named.
In the above-mentioned prior art, with respect to the display device which adheres and fixedly secures two glass plates using the outer frame, when the display device becomes large-sized, the display device is liable to be broken during handling thereof and this causes waste in processing the material used for the display thus pushing up the manufacturing cost.
To obviate such a problem, a technique which divides the outer frame into a plurality of members and then assembles and adhere these members each other may be considered. However, in such a technique, after adhering, a leaking of the inner pressure is liable to occur at portions where these members are adhered to each other so that it is difficult to maintain the air-tightness. Accordingly, it has been a task of the present invention to solve such a problem.
Accordingly, it is an object of the present invention to provide a display device which can solve the above-mentioned task of the prior art and can maintain the air-tightness of a sealed space while holding a gap between two glass plates at a given value even when the gap is large.
To achieve the above-mentioned object, the present invention provides a display device comprising a front surface panel, a back surface panel and an outer frame, wherein the front surface panel, the back surface panel and the outer frame are fixedly secured to each other by an adhesive agent, and a sealed space formed in the inside surrounded by the front surface panel, the back surface panel and the outer frame is set at a pressure lower than the outside pressure, the improvement being characterized in that the outer frame is comprised of a plurality of wall members and portions of at least some neighboring wall members which are engaged with each other have oblique surfaces at least partially, a crossing angle made by a normal line of the oblique surfaces and a normal line of the front surface panel or the back surface panel is set to an acute angle, and both oblique surface portions which are engaged with each other are fixedly secured to each other by way of the adhesive agent inserted therebetween.
Due to such a constitution, in the sealing step, the adhesive agent is coated on the oblique surface portions of the outer frames which are engaged with each other, pressure is applied to the oblique surface portions in the direction toward the front surface panel and the back surface panel, and the adhesive agent is melt by heating the adhesive agent at a high temperature. In this case, since the crossing angle made by the normal line of the above-mentioned oblique surface and the normal line of the front surface panel or the back surface panel is set to an acute angle so that a state in which the pressure is applied to both oblique surface portions is realized. Accordingly, the adhesive agent inserted between these oblique portions can be generally easily extended so that the reliable sealing is obtained. Accordingly, the leaking of the inner pressure hardly occurs so that the air tightness of the sealed space can be maintained. To the contrary, in case that the portions of the outer frames which are engaged with each other have no oblique surface portions and are set perpendicular to the front surface panel and the back surface panel, even when an adhesive agent is coated between the engaging portions and pressure is applied to these engaging portions in the direction toward the front surface panel and the back surface panel, since the pressure is not applied to the engaging portions and the adhesive agent, the adhesive agent is not smoothly extended over the entire area of the engaging portions. Accordingly, there arises a possibility that a gap is formed between the engaging portions thus accelerating the leakage of the inner pressure.
Further, when the sealed space is set at a pressure lower than the pressure of the outer atmosphere or a vacuum is produced in the sealed space, the oblique surfaces which are engaged with each other respectively receive the pressure from the back-surface-panel side and the front-surface-panel side and hence, the leaking of the inner pressure hardly occurs at the engaging portions whereby the air-tightness of the sealed space is maintained.
Still further, it is preferable to protrude the adhesive agent from an interface of the oblique portions which are engaged with each other since this makes the leaking of the inner pressure more difficult.
The sealed space at a reduced pressure may preferably be evacuated.
It is preferable that the wall members are formed of material which is equal to material of the front surface panel or the back surface panel or are formed of glass material. Further, it is preferable that the adhesive agent is formed of frit glass.
The present invention is particularly effective when it is applied to a FED which mounts field emission elements on a back surface panel and sets a gap defined between a front surface panel and the back surface panel to not less than 1 mm.
Further, it is preferable that each wall member has the oblique surfaces at both ends thereof, wherein one of the oblique surfaces formed at both ends is formed of an oblique surface which is directed toward the front surface panel and the other of the oblique surfaces at both ends is formed of an oblique surface which is directed to the back surface panel.
Further, each wall member may have the oblique surfaces at both ends thereof and both oblique surfaces at both ends may be formed of oblique surfaces which are directed to the front surface panel or both oblique surfaces at both ends may be formed of oblique surfaces which are directed to the back surface panel.
Both oblique surface portions which are engaged with each other may have a recess and a protrusion which are engaged with each other at least at a portion of the oblique surface portions.
It is needless to say that the present invention is not limited to the above-mentioned constitutions and constitutions which will be explained later and various modification may be made without departing from the technical concept of the present invention.